Re: Physical layout of a DB in RAC environment

On Fri, 30 Jan 2004 08:10:28 +0100, Roman Klesel <rupa_at_firemail.de> wrote:

>
>> Roman,
>>
>> Do you get to keep a backup set on something other than the T1 units?
>> (and I don't mean tape).
>
>I don't really understand what you mean here.
>We do an RMAN Backup to a NFS mounted Filesytem (another point that I'm
>very suspicious about.
>
>Otherwise no. Everything live and shadow DB resides on different
>partitions/RAW devices on the 2 T1s which are software mirrored.
>
>> use at least 4 redo log groups, with at least 2 members per group.
>> size the logs so that the log switches co-incide with your recovery
>> objectives.
>
>That's the case here.
>
>> If you want a log switch every 60 minutes and all of your transactions
>> occur during an 8am to 6pm window, then you could roughly estimate
>> your log size from:
>>
>> select to_char(completion_time,'Day HH24') day_hour, count(1),
>> trunc(sum(blocks*block_size)/1048576) mb,
>> round(trunc(sum(blocks*block_size)/1048576)/count(1),2) avg_log
>> from v$archived_log
>> where substr(to_char(completion_time,'Day'),1,1)!='S'
>> and to_char(completion_time,'HH24') between '08' and '18'
>> group by to_char(completion_time,'Day HH24')
>> /
>
>Thanks I will use this for optimisation. Until now I was examining the
>ceckpionts written to the alertfile in order to calculate the frequency
>of the log switches.
>
>>
>> and set the parameter archive_lag_target to the switch interval in
>> seconds (e.g. 3600).
>
>Thanks I was allready looking for the cause of the log switches every 30
>min.
>
>
>I'm quite surprised that the idea to just dump everything into a black
>box is that much accepted. I'm coming from the SAP scene and the
>performace people there still totally doom this concept. Especially
>putting Redolog files on such a box. They just hate RAID5.
>
>Roman

Sounds like they can't make the mental leap from dealing with discrete, dedicated disks to SAN units with massive amounts of parallelism. And while I've never worked with SAP, it doesn't take much reading in this very ng to see a general consensus that the app itself is a performance dog in its own right. If that is true, and based on my own experience with other app vendors, they'll look for any excuse, no matter how slim or unsubstantiated, to place performance blame somewhere outside of their app. Received on Fri Jan 30 2004 - 09:01:06 CST